This invention relates to a paper disintegrator comprising a rotor with horizontal axis rotatably journalled in a housing with filling opening and equipped with disintegrating tools, and comprising a discharge grating disposed beneath the rotor and also a discharge opening of the housing associated with the discharge grating. It relates furthermore to a method of operating this paper disintegrator. A disintegrating machine of the foregoing type, which is intended for trash and other waste materials, is described in DE-AS No. 25 16 014. With the rotor there are associated, amongst other things, a non-permeable grinding track possessing ribs oriented approximately parallel to the rotor axis and a grinding grating permeable to disintegrated material. The grinding grating possessing grating bars approximately parallel to the axis can be travelled horizontally laterally out of the lower part of the housing on rails. During operation of the machine for disintegrating normal trash, the material is first centrifuged onto an impact or rebound device situated above the grinding track and, after the corresponding pre-disintegration, is further so disintegrated on the grinding track that it can fall through the grinding grating. The grinding track and the grinding grating here surround substantially the lower half of the rotor in the aforementioned sequence. Whereas the grinding grating is intended to have a generally uniform distance from the beater circle of the rotor tools, it is intended to cause the distance between grinding track and rotor to become smaller in the rotor rotational direction. If hard objects which cannot be disintegrated are present in the material being treated, the grinding track can be temporarily swung away from the rotor.
The machine known from DE-AS No. 25 16 014 can also be used for disintegrating coarse material, such as bulky trash or rubbish, and indeed for disintegrating tough material, such as old tires. In the first mentioned case the disintegrating takes place substantially by the impact or rebound track, while the grinding grating is travelled entirely out of range of action of the rotor. The grinding track should here be disposed just sufficiently far from the beater circle of the rotor that a further granulation is carried out to a certain extent but there is no risk of jamming the machine. If, by contrast, old tires or similar tough material is to be processed, then grinding track and grinding grating are entirely removed or swung out from the range of action of the rotor and the rotor tools are brought into engagement solely with a shredder comb or with an anvil edge. For the last-named case, the rotational direction of the rotor of the known machine must be reversed. This changeover requires, however, a time consuming and energy consuming braking of the rapidly revolving rotor, revolving e.g. at 1500 rpm. Stopping of the rotor will also be necessary if the grinding grating has been moved out of the working position or been brought back into this position. Finally, a substantial disadvantage of the known machine lies in the fact that the grinding grating, when in its position moved out away from the operating position, interferes with the removal of the disintegrated material.
From the periodical "Zement-Kalk-Gips" ("Cement-Lime-Gypsum"), year 18 (1965), Vol. 11, Page 6, an impact pulverizer intended for granulating limestone and the like and having gratings in the lower part is also known. During maintenance, the grating can be withdrawn in the manner of drawers from the lower part of the impact pulverizer. During operation also, it is possible for one half of the grating basket to be pushed away from the rotor to provide an outlet gap. For reasons of space within the machine, however, only very small displacements of the grating basket halves which are divided approximately in the vertical plane through the rotor axis, can be carried out in the described example of construction. If, for example, the first grating half in the rotor rotational direction is pushed away somewhat from the rotor while the machine is operating, then a working zone converging in circular form between rotor and grating results, in which, if the machine is used for disintegrating normal trash or paper, the material increasing notably in volume during processing would become compacted and jam. If, by contrast or in addition, the second grating basket half in the rotational direction is pressed somewhat away from the beater circle of the rotor tools, then certainly a diverging wedge is produced between the rotor and the grating, but the material leaving the first grating does not even arrive in this diverging wedge but becomes jammed before the moved back second grating. The known machine is therefore unsuitable in its basic conception for disintegrating trash, paper and similar light material.
Paper disintegrators must be equally suitable for shredding individual sheets of paper, more or less large bundled stacks, entire files of documents and even material delivered in sacks. Widely varying requirements may be imposed in regard to the degree of disintegration, depending upon the type of input material. Relatively coarse disintegration is sufficient, for example, if it is only a matter of supplying the paper for further processing. In many cases smooth paper only has to be processed so that it can be pressed. Stringent requirements in regard to fineness of disintegration are, however, demanded in the destroying of secret or personnel files. The more finely the material has to be disintegrated, the greater is the time and energy required for the disintegration work. It is therefore of interest to be able to adapt the machine to the particular requirements rapidly and with the rotor still running. This is particularly so where fairly small batches of material of different types have to be processed one after another. To satisfy these requirements, it has hitherto frequently been the practice to use three shredders one after another, thus processing the material fed in by steps to the final desired state.
In paper shredders, a serious problem resulting from the low specific density of the paper shreds arises in so guiding the air in the machine that disintegrated material is blown or sucked towards the machine outlet. A feature counteracting this is that the rotor, due to its high rotational speed, generates an increased pressure on the front face (as viewed in the rotational direction) of fixed tools mounted in the beater circle of the rotor tools and a corresponding suction on the rear face of the fixed tools, as compared with ambient pressure. As a consequence pressure conditions can arise in the machine which lead to the charged material being carried immediately outwards again by an air stream oriented from the inside outwards in the inlet opening of the machine. At least it is frequently difficult to bring paper from the filling shaft of the machine into the range of action of the rotor tools.
These problems become still further intensified if, in order to achieve a uniform paper disintegration, gratings are disposed on the lower side of the rotor. This is because at the high rotational speed of the rotor the gratings can act almost like a closed plate, so that even sufficiently disintegrated paper does not fall through the grating. In practice it has therefore become usual to mount a powerful blower in the outlet of the machine, which sucks the disintegrated material through the processing range of the rotor. Since the efficiency of the machine is a function of the throughput of disintegrated material per unit of time and energy consumed, the extraction blower should only be brought into operation when this is absolutely necessary.